Ash blankets the slopes below the Te Maari crater on Tongariro, two days after the eruption.

BRUCE MERCER

The weather closes in on Tongariro as DOC and science crews fly around the crater to get a better view, two days after the eruption.

People in Blenheim have noticed a smell of sulphur gas today, linked to the Mt Tongariro eruption.

The GeoNet website alert at noon today shows Blenheim and Nelson as the southern-most centres in the wider region where volcanic ash is expected to fall.

A woman living in Rapaura said she had noticed the smell in her home about noon, while a woman said her family had noticed the smell outside early this morning.

Niwa

Infrared imaging of Tongariro ash cloud.

Niwa

Infrared imaging of Tongariro ash cloud.

Niwa

Infrared imaging of Tongariro ash cloud.

Another Blenheim woman said it was horrible.

''I closed my windows and put a plug-in smelly to get rid of it before I went to work and can't smell it anymore, thank goodness.''

Nelson Marlborough medical officer of health Ed Kiddle said he did not expect the smell to cause health problems.

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People in Rotorua probably lived with a higher level every day, he said.

''People are very sensitive to sulphur smell but the amount in the air would be tiny,'' Dr Kiddle said.

Rain in Marlborough was probably carrying the rotten egg smell associated with sulphur.

Monitoring for air pollution was unlikely to identify sulphur specifically but would pick up tiny particles in the atmosphere, he said. Health alerts surrounding the Mt Tongariro area did not mention any concerns about sulphur, but said breathing in grit-like ash could cause problems, he said.

Marlborough District Council air quality monitoring staff could not be contacted today about whether they measured sulphur or sulphur dioxide in the atmosphere.

Mt Tongariro spewed rocks and ash when it came to life for the first time in more than 100 years at 11.50pm on Monday.

GNS Science duty vulcanologist Craig Miller said it was likely the smells reported as far south as Blenheim were caused by the eruption.

"It's a little bit surprising it has gone as far as it has. It will be dissipating as it goes."

Hutt Valley resident Heidi Parker said she thought the smell was just her damp front yard at first but she could smell it all the way to work in Newtown. She said her colleagues had noticed it too.

Titahi Bay resident Robert Gibson said he and his colleagues at work had noticed the smell and were using air freshener to deal with it.

"It was a sulphury sewage-like smell. I thought my drains were blocked at first."

MetService forecaster Micky Malivuk said wind conditions were right for the smell to travel south.

Northerly winds of between 20kmh and 50kmh had been prevailing since yesterday afternoon. The smell of sulphur was also strong around Wairarapa but only faint in Hawke's Bay.

Horizons Regional Council said it had received reports of sulphur smells from throughout its territory overnight.

"While it is surprising that the sulphur has been smelt so strongly in the lower parts of our region, we don't consider it to be a cause for concern," emergency manager Shane Bayley said. Council air quality monitoring sites in Taumarunui and Taihape were not showing any sulphur.